Low temperature distributed feedback laser with loss grating and method

Abstract

A low threshold distributed feedback (DFB) laser is constructed for improved performance at subzero temperatures. A loss grating is employed to enhance the probability that lasing occurs near the short wavelength side of the stopband and to counteract the effect of negative gain tilt that occurs when DFB lasers are positively detuned. A method of making DFB lasers from wafers with improved yield for low temperature side mode suppression ratio (SMSR) is also disclosed.

What is claimed as new and desired to be protected by Letters Patent of the United States is:  
     
       1. A method of making semiconductor lasers for low temperature operation, said method comprising the steps of: 
       providing a multi-layer semiconductor structure having an active layer, a loss grating of a material having a band gap greater than a target wavelength of the semiconductor lasers, and a spacer layer, said spacer layer being located between said active layer and said loss grating; and  
       cleaving said multi-layer semiconductor structure such that opposed facets intersect said loss grating.  
     
     
       2. The method of  claim 1 , further comprising the step of locating highly reflective and anti-reflective coatings on said facets. 
     
     
       3. The method of  claim 2 , further comprising the step of forming said loss grating on a semiconductor substrate. 
     
     
       4. The method of  claim 3 , wherein said loss grating is formed by metal organic chemical vapor deposition or molecular beam epitaxy. 
     
     
       5. The method of  claim 3 , further comprising the step of forming a semiconductor cladding structure on said active layer. 
     
     
       6. The method of  claim 3 , wherein said semiconductor lasers are constructed to provide high side mode suppression in a positively detuned state. 
     
     
       7. A method of producing a plurality of distributed feedback semiconductor lasers, said method comprising the steps of: 
       providing a multi-layer semiconductor wafer having an active layer, a loss grating, and a spacer layer, said spacer layer being located between said active layer and said loss grating; and  
       cleaving said multi-layer semiconductor structure such that opposed facets intersect said loss grating, said loss grating shifting an emission spectrum of the lasers to a short wavelength side of a stopband.  
     
     
       8. The method of  claim 7 , further comprising the step of locating highly reflective and anti-reflective coatings on said facets. 
     
     
       9. The method of  claim 8 , wherein said loss grating has a grating period in the direction of light emission in the range of from about two thousand angstroms to about two thousand five hundred angstroms. 
     
     
       10. The method of  claim 9 , further comprising the step of forming said loss grating on a semiconductor substrate by metal organic chemical vapor deposition. 
     
     
       11. The method of  claim 10 , further comprising the step of forming a semiconductor cladding structure on said active layer. 
     
     
       12. The method of  claim 10 , wherein said spacer layer has a thickness in the range of from about three thousand angstroms to about six thousand angstroms. 
     
     
       13. The method of  claim 12 , wherein said lasers provide high side mode suppression when operated at less than −15° C. 
     
     
       14. The method of  claim 7 , further comprising the step of using a spectrum analyzer to identify said lasers. 
     
     
       15. A method of making semiconductor lasers for low temperature operation, said method comprising the steps of: 
       providing a multi-layer semiconductor structure having an active layer, a loss grating, and a spacer layer, said spacer layer being located between said active layer and said loss grating; and  
       cleaving said multi-layer semiconductor structure such that opposed facets intersect said loss grating, wherein said semiconductor lasers are constructed to provide high side mode suppression in a positively detuned state.  
     
     
       16. A method of producing a plurality of distributed feedback semiconductor lasers, said method comprising the steps of: 
       providing a multi-layer semiconductor wafer having an active layer, a loss grating, and a spacer layer, said spacer layer being located between said active layer and said loss grating; and  
       cleaving said multi-layer semiconductor structure such that opposed facets intersect said loss grating, wherein said distributed feedback semiconductor lasers provide high side mode suppression when operated at less than −15° C.  
     
     
       17. A method of producing a plurality of distributed feedback semiconductor lasers, said method comprising the steps of: 
       providing a multi-layer semiconductor wafer having an active layer, a loss grating, and a spacer layer, said spacer layer being located between said active layer and said loss grating; and  
       cleaving said multi-layer semiconductor structure such that opposed facets intersect said loss grating, wherein respective phase relationships between said opposed facets and said loss grating are such that said lasers have a lasing symmetry L sym  that is greater than 0.5.  
     
     
       18. The method of  claim 17 , further comprising the step of locating highly reflective and anti-reflective coatings on said facets. 
     
     
       19. The method of  claim 18 , wherein said loss grating has a grating period in the direction of light emission in the range of from about two thousand angstroms to about two thousand five hundred angstroms. 
     
     
       20. The method of  claim 19 , further comprising the step of forming said loss grating on a semiconductor substrate by metal organic chemical vapor deposition. 
     
     
       21. The method of  claim 20 , further comprising the step of forming a semiconductor cladding structure on said active layer. 
     
     
       22. The method of  claim 20 , wherein said spacer layer has a thickness in the range of from about three thousand angstroms to about six thousand angstroms.